EP0137470A2

EP0137470A2 - Intake system for internal combustion engine

Info

Publication number: EP0137470A2
Application number: EP84111962A
Authority: EP
Inventors: Yoshiyuki Tanabe; Mineo Kashiwaya; Kiyomi Morita; Kazunobu Kameta
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1983-10-07
Filing date: 1984-10-05
Publication date: 1985-04-17
Also published as: EP0137470A3; US4584981A; KR850003931A; DE3479231D1; JPH0211734B2; JPS6079162A; EP0137470B1; KR920002515B1; CA1221590A

Abstract

An intake system for an internal combustion engine has a fuel injector (4) disposed in an induction passage (2) upstream of a pivotally mounted throttle plate (3) having an idle position in which the throttle plate (3) has upstream and downstream edge portions slightly spaced from the inner peripheral surface of the induction passage to define therewith narrow gaps (10) for the passage of air and injected fuel particles. A bypass air passage (2) is formed in the peripheral wall of the induction passage and has a downstream end (15) open thereto to produce a jet of air directed toward the central zone of the downstream face of the throttle plate when in the idle position. The air jet is operative to compensate for the difference in pressure between a central space immediately downstream of the throttle plate and peripheral zones adjacent to the narrow gaps whereby whiriing-up of air and fuel particles just downstream of the throttle plate and resultant formation of drops of liquid fuel can be prevented.

Description

FIELD OF THE INVENTION

The present invention relates to an intake system for internal combustion engines and, more particularly, to an engine intake system of the type that employs a single or a plurality of fuel injectors disposed in an induction passage upstream of a throttle valve to inject jets of fuel into the induction passage.

SUMMARY OF THE INVENTION

The present invention has an object to provide an intake system for an internal combustion engine which is improved to assure a stable engine idle operation.
The intake system for an internal combustion engine according to the present invention comprises:

means defining an induction passage;
a throttle valve disposed in the induction passage;
at least one injector disposed in the induction passage upstream of the throttle valve and so arranged as to inject a jet of fuel therein;
the throttle valve being movable between idle and wide-open positions, the throttle valve when in the idle position having an edge portion slightly spaced from the inner peripheral surface of the induction passage to define therewith a narrow gap for the passage of air and fuel for an engine idle operation; and
means defining an air passage extending in bypassing relationship to the narrow gap and terminating in a downstream air outlet end arranged to direct a jet of bypassing air substantially toward a central space immediately downstream of the throttle valve when in the idle position.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an axial sectional view of the prior art intake system;
Fig. 2 is a similar view but shows an embodiment of the intake system for an internal combustin engine according to the present invention;
Fig. 3 is a cross-section taken along line III - III in Fig. 2;
Fig. 4 is similar to Fig. 2 but illustrates a modification to the embodiment shown in Fig. 2;
Fig. 5 shows a modification to the embodiment shown in Fig. 3; and
Fig. 6 is similar to Figs. 2 and 4 but illustrates another embodiment of the invention.

DESCRIPTION OF THE PRIOR ART

Japanese Pre-Examination Patent Publication No. 79666/83 discloses an intake system for an internal combustion engine which system includes a single or a plurality of fuel injectors for injecting jets of fuel into an induction passage upstream of a throttle valve disposed therein. The throttle valve is rotatable about the axis of a throttle shaft between idle and fully opon positions. When the engine is in its idle operation, the throttle valve is inclined to the axis of the induction passage and has upstream and downstream edge portions slightly spaced from the inner peripheral surface of the induction passage to cooperate therewith to define narrow gaps through which air and the injected fuel particles are allowed to pass toward engine cylinders. A part of the air and fuel particles then whirls toward the center of the underside of the throttle valve due to vacuum immediately downstream of the throttle valve whereby vortices are generated downstream of the throttle valve. The fuel particles suspended in the whirling air streams tend to be gathered at a central zone of the vortices to form a mass of liquid fuel. When the liquid mass has grown to a certain size, a part of the liquid mass is separated therefrom to form drops which are sucked into the engine. For this reason, the fuel is not fed into the engine at a uniform rate all over an idle operation, resulting in unstable engine idle operations and difficulties in the emission control, as will be discussed in more detail hereunder with reference to Fig. 1 which shows a typical one point fuel injection type intake system of the prior art.
The prior art intake system shown in Fig. 1 has a throttle valve 3 formed by a circular throttle plate mounted on a rotatable throttle shaft 3a extending diametrically through an induction passage 2 a part of which is defined in a throttle body 1. A fuel injector 4 is supported by a holder 4a disposed centrally of a venturi chamber 4b to cooperate therewith to define an annular venturi 9 which forms a part of the induction passage 2. A bypass air passage 7 is formed in the peripheral wall of the venturi chamber 4b and has an upstream end open to a part 8 of the induction passage situated upstream of the venturi 9. The downstream end of the bypass air passage 7 is open to the venturi 9.
A conventional electric air flow meter 5 is attached to the outer peripheral surface of the venturi chamber 4b and includes a hot-wire type air flow sensor or temperature-sensitive resistor 5a disposed in the bypass air passage 7 to meter the flow of air therethrough and thus to determine the total air flow through the induction passage into an associated engine (not shown). The air flow meter 5 produces an electric signal representive of the rate of air flow into the engine and emits the signal to a computor 6 which is operative in response to the input signal to compute the rate of fuel supply optimum to the rate of air supply to the engine for thereby emitting fuel supply signals to the injector 4. The injector 4 is responsive to the fuel supply signals from the computor 6 to inject jets of liquid fuel into the induction passage 2 so that the engine is supplied with a mixture of air and fuel at an air/fuel ratio most suited to the engine operation.
In the intake system of the type described above, when the throttle plate 3 is in its idle position shown in Fig. 1, the air and the fuel particles passing through narrow gaps 10 defined between the upper (upstream) and lower (downstream) edge portions of the throttle plate 3 are whirled toward the central zone of the induction passage 2 immediately below the throttle shaft and downstream of the throttle plate 3, as schematically illustrated in Fig. 1. This is because of the difference in pressure between the sections of the induction passage 2 adjacent to the narrow gaps 10 and the central section of the induction passage just downstream of the throttle plate 3. The whirled air streams and fuel particles are gathered to a central space of the induction passage just downstream of the throttle valve 3. The fuel particles thus gathered form a mass of liquid fluid. When the liquid mass has grown to a certain size, a part of the liquid fuel is separated from the mass to form drops 11 which are then fed into the engine. The formation of the liquid mass is quire undesirable to engine idle operations because the addition of the fuel drops 11 to continuous supply of normal air-fuel mixture to the engine is discontinuous and causes a non-uniform rate of fuel supply during an engine idle operation, resulting in an unstable idle operation of the engine, and because the introduction of the liquid fuel drops into the engine increases the CO and HC contents of the engine exhaust gases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described with reference to Figs. 2 to 6 of the drawings wherein the parts and elements the same as in the prior art shown in Fig. 1 are designated by the same reference numerals. Only the improvement of the invention over the described prior art will be described hereunder for the purpose of simplifying the description.
The improvement of the embodiment of the present invention shown in Figs. 2 and 3 comprises an air passage 12 formed in the peripheral wall of the throttle body 1 and extends in bypassing relationship to the gap 10 defined between the inner peripheral surface of the throttle body 1 and the upward edge portion of the throttle valve 3 when it is in its idle position. The bypass air passage 12 has its upstream end 13 open to the induction passage 2 at a point disposed radially outwardly of the cone of the jet of fuel injected by the fuel injector 4. In the illustrated embodiment of the invention, the downstream end 15 of the bypass air passage 12 is open to the induction passage 2 at a point downstream of the upstream edge portion of the throttle valve 3 when in its idle position and directed substantially toward the central zone of the undersurface or downstream face of the throttle valve 3.
Thus, when the engine is in its idle operation, a part of the air which has passed through the venturi 9 enters the bypass air passage 12 and flows therethrough in bypassing relationship to the flow of air and fuel particles passing through the gap 10. The bypass air is then jetted through the downstream end 15 of the bypass air passage 12 into the induction passage 2 downstream of the throttle valve 3. The jet of air is directed substantially toward the central zone of the downstream face of the throttle valve 3 to eliminate or compensate for the difference in pressure between the induction passage 2 just downstream of the throttle valve 3 and the sections of the induction passage 2 adjacent to the gaps 10 which difference would otherwise be caused due to the reason discussed above in'connection with the prior art. Accordingly, the air and fuel particles which have passed through the gaps 10 flow smoothly toward the engine and will not be whirled up to the center of the induction passage 2 immediately downstream of the throttle valve. For this reason, the production of a liquid mass and resultant formation of fuel drops, which have taken place in the prior art, are advantageously avoided to assure a stable fuel supply to the engine at a substantially constant rate all over an engine idle operation for thereby insuring a stable engine idle operation and minimized emission of CO and HC.
It will be appreciated that, because the upstream end 13 of the bypass air passage 12 is disposed outwardly of the cone of the jet of fuel injected by the injector 4, the air flowing through the bypass air passage 12 and jetted through the downstream end 15 thereof does not contain any amount of fuel. Thus, the inner peripheral surface of the induction passage 2 downstream of the downstream end 15 of the bypass air passage 12 is prevented from being adhered by any liquid film or drops of the fuel which would oterwise flow through the bypass air passage 12. Such a liquid film or drops of fuel cannot easily be atomized and thus will adversely affect the engine operation and emission control.
In addition, the upstream end 13 of the bypass air passage 12 is located downstream of the downstream end 14 of the first bypass air passage 7 which contains the temperature-sensitive air flow sensor element 5a. Thus, the part of the air flow which passes through the second bypass air passage 12 is included in the total air flow to the engine which has already been measured by the air flow meter 5. This feature is advantageous in the view point of air-fuel ratio control.
The position of the downstream end 15 of the bypass air passage 12 is important to attain the intended purpose. In the embodiment of the invention shown in Fig. 2, the downstream end 15 is positioned at a level substantially the same as the level of the downstream edge portion of the throttle valve 3 when in its idle position. However, in the modification shown in Fig. 4, the downstream end 15 of the bypass air passage 12 is located. immediately or slightly below the upstream edge portion of the throttle valve 3 when in the idle position. The bypass air passage downstream end 15, however, is not limited to the positions shown in Figs. 2 and 4 and can be located at any point within the distance or range defined between the positions shown in Figs. 2 and 4.
Secondly, the bypass air passage downstream end 15 should be open in the induction passage 2 on the side thereof substantially aligned with the upstream edge portion of the throttle valve 3 as viewed in the flow of air through the induction passage 2, namely, on the righthand side of the induction passage 2 as viewed on the illustrations in Figs. 2 and 4. If the downstream end 15 of the bypass air passage 12 were formed in the lefthand side of the induction passage 2, i.e., adjacent to the downstream edge portion of the throttle valve 3, the air jetted from such a downstream end will not be operative to prevent the downsteram face of the throttle valve 3 from being adhered by fuel particles.
In the embodiment of the invention shown in Fig. 2 and the modification shown in Fig. 4, the downsteam end 15 of the bypass air passage 12 is in the form of a circular opening 15A, as shown in Fig. 3. In the modification shown in Fig. 5, however, the bypass air passage downstream end 15 is in the form of an arcuate slit or groove 15B formed in the inner peripheral surface of the throttle body 1 and extending circumferentially thereof over a predetermined angle. The opposite ends of the length of the groove 15B are shaped to direct air substantially toward the central area of the undersurface or downstream face of the throttle valve 3 when it is in its idle position.
When the throttle valve 3 is in a wide-open position, the pressure in the induction passage 2 downstream of the throttle valve is substantially equal to the pressure in the induction passage 2 upstream of the throttle valve 3. In such an engine operating condition, therefore, little air flows through the bypass air passage 12. Thus, the flow of air through the bypass air passage 12 takes place only when the pressure differential across the throttle valve 3 exceeds a predetermined level.
In the second embodiment shown in Fig. 6 of the drawings, an air nozzle 17 is fitted into the downstream end of the bypass air passage 12 and extends inwardly from the inner peripheral surface of the throttle body 1 substantially toward the center of the bypass air passage 2. The air nozzle 17 is provided with nozzle orifice 17A adjacent to the inner end of the nozzle 17. The air entering the bypass air passage 12 is jetted through the nozzle orifice 17A to the central space of the induction passage just downstream of the throttle valve to reliably compensate for the diference in pressure between the central space of the induction passage immediately downstream of the throttle valve 3 and the peripheral zone of the induction passage 2 adjacent to the gaps 10, whereby the whirling-up of the air and fuel particles just downstream of the throttle valve is prevented. The nozzle orifice 17A adjacent to the inner end of the air nozzle 17 defines the narrowest section of the bypass air passage 12, so that the air is jetted through the nozzle orifice 17A substantially at sonic velocity. The sonic air jet, therefore, is operative to atomize the fuel particles in the induction passage just downstream of the throttle valve to thereby improve the stability of the engine idle operation.
As described above, the intake system according to the present invention is efective to prevent the formation of drops of fuel during engine idle operations for thereby ensuring smooth engine idle operations and reduced emissin of CO and HC during engine idle operations.

Claims

1. An intake system for an internal combustion engine, comprising:

means defining an induction passage;

a throttle valve disposed in said induction passage;

at least one injector disposed in said indue- tin passage upstream of said throttle valve and so arranged as to inject a jet of fuel therein;

said throttle valve being movable betwen idle and wide-open positions, said throttle valve when in said idle position having an edge portion slightly spaced from the inner peripheral surface of said induction passage to define therewith a narrow gap for the passage of air and fuel for an engine idle operation; and

means defining an air passage extending in bypassing relationship to said narrow gap and terminating in a downstream air outlet end arranged to direct a jet of bypassing air substantially toward a central space immediately downsteram of said throttle valve when in said idle position.

2. An intake system for an internal combustion engine, comprising:

means defining an induction passage;

a throttle valve comprising a throttle plate pivotally mounted in said induction passage by a throttle shaft extending substantially diameterically therethrough;

at least one fuel injector disposed in said induction passage upstream of said throttle valve and so arranged as to inject a jet of fuel therein;

said throttle valve being rotatable about the axis of said throttle shaft between idle and fully-open positions, said throttle valve when in said idle position being inclined to the axis of said induction passage and having upstream and downstream edge portions slightly spaced from the inner peripheral surface of said induction passage to cooperate therewith to define narrow gaps for the passage of air and fuel therethrough for an engine idle operation; and

means for producing a jet of air directed toward the downstream face of said throttle valve when the intaken vacuum downstream of said throttle valve exceeds a predetermined level.

3. An intake system according to Claim 2, wherein said induction passage defining means include a throttle body having said throttle valve mounted therein, and wherein said air jet producing means include an air passage extending through said throttle body in bypassing relationship to said throttle valve and having an upstream end open to said induction passage upstream of said throttle valve when in said idle position and disposed such that the fuel injected by said fuel injector does not enter said bypass air passage, said bypass air passage having a downstream end operative to direct a jet of air toward said downstream face of said throttle valve.

4. An intake system according to Claim 3, wherein said downstream end of said bypass air passage is open to said induction passage downstream of said upstream edge portion of said throttle valve when in sad idle position but upstream of said downstream throttle valve edge portion when said throttle valve is in said idle position, said downstream end opening of said bypass air passage being directed substantially to the central area of said downstream face of said throttle valve when in said idle position.

5. An intake system according to Claim 4, wherein said downstream end opening of said bypass air passage is generally circular.

6. An intake system according to Claim 4, wherein said downstream end opening of said bypass air passage is in the form of a groove formed in the inner peripheral surface of said throttle body and extending in the circumferential direction thereof.

7. An intake system according to Claim 3, wherein said downstream end of said bypass air passage comprises an air nozzle extending radially inwardly of said induction passage substantially toward the central zone of said downstream end face of said throttle valve when in said idle position.

8. An intake system according to Claim 7, wherein said nzzle has restricted nozzle orifice formed therein adjacent to an end thereof remote from the throttle body inner peripheral surface.

9. An intake system according to Claim 2, further including means metering the rate of air flow through said induction passage into said engine and producing an electrical signal representing the air flow rate thus measured and means responsive to said signal to electrically control the operation of said injector so that the fuel is injected by said injector at a rate substantially proportional to the rate of air flow into said engine.

10. An intake system according to Claim 9, further including means supporting said injector in said induction passage upstream of said throttle valve, and said supporting means defining therein a venturi forming a part of said induction passage upstream of said throttle valve and an additional air passage having an upstream end open to said induction passage upstream of said venturi and a downstream end open to said venturi, and wherein said air flow metering means include a heat- sensitive resistor disposed in said additional air passage to detect the velocity of air flow therethrough to thereby meter the rate of total air flow through said induction passage into said engine.